We construct a higher Whitehead torsion map, using algebraic K-theory of spaces, and show that it satisfies the usual properties of the classical Whitehead torsion. This is used to describe a 'geometric assembly map' defined on stabilized structure spaces in purely homotopy-theoretic terms.
IntroductionGiven a space X, the structure space S n (X) is the space of all homotopy equivalences M → X, where M is an n-dimensional manifold (of some given type, such as compact or closed, differentiable, piecewise-linear, or topological). Obviously, X has the homotopy type of such a manifold if and only if the structure space of X is non-empty. In this case, π 0 S n (X) is the central object of interest for the classification of manifolds in the homotopy type of X; the higher homotopy type of S n (X) is closely related to the study of automorphisms of these and to the classification of families of manifolds homotopy equivalent to X [23].If p : E → B is a given fibration, then the above construction can be generalized as follows: A point in the structure space S n (p) of p is given by a bundle of n-dimensional manifolds E → B over B together with a fibre homotopy equivalence E → E. (So the structure space of the space X is the structure space of the trivial fibration X → * .) Pull-back defines a pairing S n (B) × S k (p) −→ S n+k (E), thus if B comes with a given structure, then evaluation of this pairing defines a map α : S k (p) −→ S n+k (E).Geometrically, this map assembles all the manifold structures on the individual fibres to one manifold structure on E, so we call it the geometric assembly map. It is relevant, for instance, in the study of fibring questions.Algebraic K-theory of spaces [19] is a key tool in understanding families of manifolds. The connection to the topology of manifolds is established by the stable parametrized h-cobordism theorem [20], which classifies families of h-cobordisms in terms of K-theory, in a stable range. Recently, Hoehn [7] has used the stable parametrized h-cobordism theorem to describe the homotopy type of the stabilized structure space S ∞ (p) := colim S n (p)